Saturday, July 18, 2015

Indigo 2015: The vat

I've been lazy about blogging, but I've been busy with this summer's indigo dyeing.  This year I'm trying a zinc-lime vat, which takes time to set up, but is supposed to produce deeper, richer blues than the thiox vat.  In mid-June, I prepared my first stock solution:

The stock looked really good after five hours of reduction--the dark amber color was just what it's supposed to be, and there was a good, thick layer of  indigo "flower" with a nice bronze sheen on top.

This vat uses zinc as a reducing agent in combination with calcium hydroxide (lime).  Although the zinc-lime vat has a reputation for being a bit tricky to manage, it has a number of advantages in addition to the colors that it produces.  It reduces indigo efficiently, works at room temperature down to about 60 Fahrenheit, and can be revived even after months of non-use.  Unfortunately, as I noted in an addendum to a previous post, the zinc is rated as a hazard for aquatic life, so the vat has to be disposed of properly as hazardous waste and can't be poured down the drain.  In the longer term, if I want a room temperature vat, I'll have to switch to a ferrous sulfate vat.  It doesn't have the efficiency and longevity of the zinc-lime vat, but is better for the environment (at least as far as anyone knows at the moment).

I had difficulty with the vat for the first several days.  Various dyeing guides talk about looking for a "French mustard" color or a color ranging from yellow to dark amber, depending upon the amount of indigo in the vat.  I thought I had a vat on the yellow-ish side when I first started dipping, but after several rounds, I didn't seem to be building additional color, and my first fabrics weren't very well dyed.  In retrospect, I think the vat was too green and the indigo wasn't reduced enough.  The initial vat also didn't stay chemically balanced as long as I thought it would, and when I went away for a weekend after the first few days of dipping, the vat died completely.  I fiddled with sharpening the vat by adding various combinations of additional zinc, lime, and indigo, and eventually, after about ten days after the original stock solution, I got the following result:

At this point, the vat seemed very bubbly and lively, with lots of dark blue "flower," flecked with bronzy blue bits.  The vat liquid itself reached a perfect dark amber, and I felt certain it was just right.  I immediately started dyeing some elaborate nui shibori pieces that I had laboriously stitched and tied a while back, but didn't dare dye until I felt confident about the vat.

I'll discuss the results of my initial round of dyeing in the next few posts.  Indigo Summer 2015 is well underway!

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